Orthodontics · single question
The orthodontic extrusion rate of the maxillary central incisor is approximately:
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Correct answer: B. 1 mm per month
Forced orthodontic extrusion (eruption) of a tooth for pre-prosthetic purposes proceeds at approximately 1 mm per month (or 0.25-0.5 mm per week with proper force application). This is consistent with the rate of physiologic tooth movement — too rapid extrusion risks fibrous tissue following the tooth without proper bone deposition. The standard protocol is gradual extrusion to allow bone to follow.
- A. INCORRECT. 2 mm per week is excessive and would cause irreversible damage to the PDL and bone.
- B. CORRECT. Approximately 1 mm per month is the standard rate for forced orthodontic extrusion. This allows both the PDL fibers and alveolar bone to remodel and follow the tooth being extruded.
- C. INCORRECT. 1 mm per week is too rapid for safe forced extrusion. This rate would likely result in fibrous tissue remodeling without proper bone deposition, creating a soft tissue pocket rather than bone support.
- D. INCORRECT. While 2 mm per month is within the possible range for some cases, 1 mm per month is the more conservative standard teaching for predictable bone deposition.